Information codes such as barcode and QR code (registered trademark) have found use in a variety of applications. PTL 1 discloses an information code forming medium on which an information code is printed with a second ink in an area printed with a first ink to provide enhanced security of the information code. The first ink is imaged as transparent when irradiated with infrared radiation, and the second ink is imaged as dark color when irradiated with infrared radiation. Information code in the information code forming medium is embedded in a background and becomes invisible in an environment where the code is irradiated with visible radiation.
On the other hand, an image processing technology has been heretofore proposed to recognize a two-dimensional code by imaging the code with a video camera and show, on a display device, a three-dimensional image appropriate to the two-dimensional code. PTL 2 discloses a rectangular card that includes a two-dimensional code that in turn includes a reference cell, a code data portion, and a plurality of corner cells arranged in such a manner as to enclose the code data portion.